Fire-resisting containers



June 2, 1964 G. H. BULMER 3,135,419 FIRE-RESISTING CONTAINERS Filed May 4, 1962 w FIRE-RESISTING CONTAINERS George Henry Bulmer, Culcheth, near Warrington, England; assignor. to United Kingdom Atomic Energy Authority, London, England 5 Filed May 4, 1962, Ser. No. 192,394 Claims priority, application Great Britain May 5, 1961 1 6 Claims. (Cl. 220-63) 1 The storage and conveyance in closed containers of solid pyrophoric materials gives rise'to the problem that if by misadventurethe contents should ign te the onset of fire may go unnoticed until the integrity of the container is in danger and the release ofburning material 1s imminent. I j

:Containers embodying various inert powdered substances have been used hitherto to aiford thermal insulation or" fire suppression or bgth. With powdered substances-jthe occurrence of a fire may leave the powder form unchanged in which case oxygen for supporting the fire'can diifuse'through the interstices of the powder particles; if temperatures are developed exceeding the melting'pointof the substance concerned, the powder loses volume by fusion andhence the; covering potential 18 diminished.

According to thepresent invention, there is provided a container lined with a solid fused layer of a fire extinguishing agent based on a mixture ofinorgamc salts,

- such layer being separated from the free interiorspace of the container by a membrane collapsible by heat. Be-- sides being rendered fire-resisting in this way, such a container is effective inherently to extinguish, or at least suppress, an internal outbreak of fire in that the fire extinguishing agent of the lining layer becomes molten and will spread into contact with the burning material once the separating membrane has broken down. This separating'membrane is to be understood in the present context to be susceptible to collapse under the action of heating, it serves to keep the container contents free from contamination bythe fire extinguishing agent and also to protect the latter from being rubbed and chipped. During manufacture, the separatingmembrane may be used to define a mould cavity in which the lining is cast directly within the container. I 1

Low melting point fire extinguishing agents are preferred, such as are quoted in the specificationsof co-pending applications Serial Nos. 40,530,, now Patent No. 3,096,372, and 176,799, owned by the assignee of the instant invention, where a melting point of less than 640 C. is specified in order particularly, to meet the needs of a" fire involving plutonium which becomes molten at about this point. Mixtures of inorganicchloride and/ or fluoride salts of the alkalimetals and the alkaline earth metals are, given as examples in these specifications.

The solid fusedlining of the firefextinguishing agent enables the accommodation in a lining layer of given dimensions of a, greater weight of'the agent than if the power form were to be used The following figures in respect of a eutectic mixture of the chlorides of sodium, potassium and barium will illustrate this point:

' Those of these measurements which relate to the pow der form of the mixture were made on samples having atypical degree of fineness'for fire extinguishing purposes; this may be expressed as an area of the order of United States Patent ice 1,500 sq. cm. covered by one gm. The solid fused form, being less pervious, is also better adapted to resist absorption of atmospheric moisture which for certain types of fire, notably those involving certain nuclear reactor ma-' tcrials, promotes violent oxidation.

A further preferred feature of the invention, however, is that the lining layer of fire extinguishing agent is sealed permanently from contact with atmospheric air.

- In the particular embodiment of the invention which is illustrated in the accompanying drawing the container has an outer wall constituted by a cylindrical drum 11 of mild steel 0.048 inches thick having twin girth ribs 12 and 13, the drum having a lapped stitch-welded seam (not appearing in the drawing) and a rolled seal bottom as indicated at 14'. A lid- 15 for closure of the open top of the container has a a peripheral lip co-operating with a corresponding outwardly, directed lip formed at the top of the drum; and isreinforced at its inside surface by a flat ring 16 of mild steel inch thick and at its outside surface tomary to lock in the clasped position bya turn or so of wire with a seal when the container is charged.

A first liner 20 disposed within the drum 11 is of thin mild steel, say 0.001 inch thick, and leaves between itself and both the side wall and the bottom of the drum a space about one inch wide which is packed with athe'rmally insulating interlayer 21 of a granular material, such as diatomaceous earth, kieselguhr or exfoliated vermiculite. An annular retaining cover 22 of mild steel extends over the interlayer at the top edge of the liner 21, the fixture of this cover being preferably by spotwelding so as to allow intercommunication between the interlayer. and the outside space.

A second liner 23 disposed within the drum 11 leaves between itself and both the side wall and the bottom of the first, liner 20 a space about 1 /2 inches wide. This second liner may be also of a thin metal sheet, such as mild steel, but in order to be more readily collapsible by heat it is preferably of a stiif section of synthetic thermoplastic resin. The space between the two liners is occupied with a solid fused layer 24 of a low melting point fire extinguishing agent based on a eutectic mixture of inorganic salts, the following being two leading examples of the compositions that are suitable:

Percent Example 1: a NaCl 20 KCl 29 BaCl 51 f Example 2:

LiF- 29 NaF '12 KF 59 melting point'of the first is about 545 C. and of the sec- The percentages quoted above are by Weight. The

ond about 454 C. Additions to promote free flow, such ,astalc and metallic soap, are unnecessary in the present I application, although for drying purposes a metallic soap addition, for example. about 2 /2 by weight of magnesium stearate, may still be desirable. More positive protection against absorption of atmospheric moisture is afforded by a sealing layer 25 laid over the upper end of i of a synthetic resin impervious to moisture such as one of the epoxy range as used for the encapsulation of components.

Advantageouslythe fused layerZd is installed by the following procedure: As a first step there is deposited in the bottom of the container with the first liner 20 and thermally insulating layer 21 already installed, a shallow bed of molten fire extinguishing agent at least to the thickness required at the bottom. During cooling of this bed, and whilst it is still plastic, the second liner 23 is inserted concentrically into the container and pressed down if necessary into the bed to give the requisite thickness of underlying fire extinguishing agent. The two liners now definea mould cavity for casting the further part of the lining layer. Further fire extinguishing agent of the same composition is now introduced in'a molten condition to fill this cavity and is allowed to solidify with the second liner remaining in position to act as a conti'guous membrane separating the side wall lining of fire extinguishing agent from the free interior space of the container. extinguishing agent in powder form may be placed over the contents in a bag or sachet.

Typical dimensions for the illustrated container are a height of about 28 inches and an outside diameter of membrane means spaced inwardly from said first-mentioned means for forming the interior Walls of the container and for collapsing under heat generated in themterior of the container; and a solid fused layer of a fire When the container is in use additional fire" extinguishing agent based on a mixtureof inorganic salts disposed in the space defined between said means forming said outer, walls and said means forming said interior walls.

2. A container as claimed in claim 1 having an open top closable by a lid, said membrane means being in the form of a cup-shaped liner of asynthetic thermoplastic resin which is contiguous with said fire extinguishing agent lining the sides and bottom of the container.

3. A container as claimed in claim 1, in which said fire extinguishing agent has a melting point bel0w'640'C.

4. A container as claimed in claim 3, in which said salt mixture is of inorganic salts selected from the class consisting of the chlorides and fluorides of the alkali metals and the alkaline earth metals.

5. A container as claimed in claim 1, further comprising means for permanently sealing said solid fused layer from contact with atmospheric air. 1

'6. In a containensuitable for the storage and conveyance of solid pyrophoric material and having an open top closable by a lid, the combination comprising two lining layers, the outer being of thermally insulating material in granular form and the inner of a solid fused mass of a fire extinguishing agent'which is based on a mixture of inorganic salts and has a melting. point below 640 C., a first liner separating the two lining layers, and a second liner contiguous with the inner lining layer and separating it from the free interior space of the container, the second liner being collapsible by heat.

References fitted in the file of this patent UNITED STATES PATENTS 

1. A CONTAINER SUITABLE FOR THE STORAGE AND CONVEYANCE OF SOLID PYROPHORIC MATERIAL, COMPRISING: MEANS FORMING THE OUTER WALLS OF SAID CONTAINER; SUBSTANTIALLY IMPERVIOUS MEMBRANE MEANS SPACED INWARDLY FROM SAID FIRST-MENTIONED MEANS FOR FORMING THE INTERIOR WALLS OF THE CONTAINER AND FOR COLLAPSING UNDER HEAT GENERATED IN THE IN- 